Generally, a chronic diabetic must perform self blood glucose monitoring at home daily to maintain constant blood glucose. In order to do a blood glucose test, a sample of blood must be drawn from a body site. For example, a disposable lancet is driven to puncture skin at a selected body site, such as fingers, thus drawing a small amount of capillary blood. The sample of blood is applied to a strip. Next, the strip is placed in a test sensor to monitor blood glucose.
In order to draw blood from a body site, a lancing device has been widely used. The lancing device includes a lancet holder, an end cap, a spring, and a trigger. A disposable lancet is secured to the lancet holder. The end cap covers the lancet, and has a hole so that a tip of the lancet is propelled to the outside of the hole, thus puncturing the skin. Further, the spring and the trigger provide skin penetration force. The lancing device is used as follows. First, the end cap is removed from the lancing device, and the lancet is inserted in the lancet holder to compress the spring. In such a state, the end cap is closed. After assembly is completed, the lancing device comes into close contact with a body site having many capillary vessels, such as a finger. In such a state, a trigger switch is pressed to activate the lancet, thus puncturing the skin at the selected body site. At this time, an area around the puncture site is compressed, thus allowing a sufficient amount of capillary blood to be obtained. The sample of capillary blood is applied to a strip of a test sensor, and then blood glucose is measured. The method of drawing blood from the capillary vessels has been most widely used, but has a problem in that a patient must always carry the lancing device and a plurality of lancets.
In order to solve the problem, a disposable auto-lancet having a trigger is disclosed in Korean Patent Appln. No. 2000-55280. Such a disposable auto-lancet is advantageous in that there is no need to carry the lancing device. However, the disposable auto-lancet is problematic in that manufacturing costs thereof increases, thus imposing an economic burden on patients. Further, the conventional lancing device is problematic in that it is possible to draw blood only from a body site having many capillary vessels, for example, fingers or toes, so that a user experiences considerable pain due to nerve fibers which are distributed together with the capillary vessels, during the puncture of skin. Thereby, the conventional lancing device or the disposable auto-lancet causes anxiety to the user, such as a chronic diabetic who draws blood every day.
Recently, in order to solve the problems, a vacuum assisted lancing device is disclosed in U.S. Pat. No. 6,152,942. The vacuum assisted lancing device punctures skin at a body site having relatively few capillary vessels and nerve fibers, for example, an arm and a thigh, and then draws blood from the puncture site under vacuum pressure. The method of using the vacuum assisted lancing device is as follows. First, an end cap is removed from the lancing device, and a lancet is inserted in a lancet holder. Next, the end cap is closed again and then turned to a predetermined position on a ramp, thus adjusting a skin penetration depth. After the lancet has been mounted in the lancet holder, an end of the lancing device comes into close contact with the skin, and a plunger is pressed. At this time, the plunger is thrust into the lancing device to compress a spring which is placed in the lancing device. Simultaneously, a one-way check valve is opened, thus displacing air in the lancing device in proportional to the compression of the spring, therefore preventing internal pressure from increasing. By the movement of the plunger, the lancet moves to a predetermined position. At this time, drive and return springs and an actuator are operated, so that the lancet punctures the skin at a desired body site and then returns to an original position thereof.
As such, when the lancet punctures the skin and then the plunger is released, the spring pulls the plunger to create a vacuum in the end cap. At this time, the lancet is removed from the skin together with the plunger. When the plunger and the lancet are retracted from the skin, the skin bulges into the end cap due to the vacuum suction and blood is drawn from the skin. Thereafter, the plunger is pressed down to release the vacuum, and the lancing device is removed from the skin. Next, the blood is touched with a test sensor, thus monitoring blood glucose.
However, the conventional vacuum assisted lancing device has a problem in that the plunger must be pressed down to release the vacuum after blood has been drawn from a desired body site, so that the lancet coupled to the plunger may undesirably rebound and cause a second puncture. Such a second puncture may cause infection.
The conventional vacuum assisted lancing device has another problem in that the depth of penetration of the lancet into the skin is limited by the ramp of the end cap, so that special care is required to mount the end cap to a housing. Thus, whenever blood is drawn from a selected body site, the penetration depth must be re-adjusted.
Further, the conventional vacuum assisted lancing device obtains energy for compressing the spring and moves the lancet to a predetermined position, when the plunger is pressed down to create a vacuum. However, since the spring is strong, the plunger must be pressed with strong force to create a sufficient vacuum. Thus, this may cause anxiety about the skin puncture in a patient, thus provoking distaste for the use of the lancing device.
The conventional vacuum assisted lancing device has a further problem in that it is exclusively used for drawing blood from a desired body site under vacuum pressure, so that the lancing device cannot be used to draw blood from a body site having many capillary vessels, such as fingers or toes.